These are known in the prior art plain paper electrostatic copying machines in which a drum carries a surface coating of photoconductive material, such for example as selenium. In operation of such a machine the surface of the drum is moved successively past the charging station at which a corona applies a uniform electrostatic charge over the surface of the drum and then to an exposure station at which the charged surface is exposed to an image of the original to be copied. At this station, the surface of the drum over relatively light areas of the image to be copied loses its charge while retaining its charge in relatively darker areas of the original, thus to produce a latent electrostatic image of the original to be copied.
Following the exposure station, the surface is carried through a developer station at which the latent image is subjected to the action of the developer including toner particles which adhere to the charged areas of the image, thus to develop the image. As the surface carrying the developed image leaves the developer station, it moves past a point at which a length of copy material, such as ordinary paper to which the image is to be transferred is fed to the drum so as to be carried along with the drum beneath a transfer corona. This transfer corona causes the particles of toner to migrate from the surface of the photoconductor to the surface of the copy sheet.
After the image has thus been transferred to the length of copy material, it is necessary to remove the sheet from the surface of the photoconductor which may, for example, be on a drum. In one particular arrangement employed to pickoff a copy sheet carrying a developed image in a machine of the type described above, a stationary flexible band conforming to the configuration of the drum over a portion of the circumference thereof from the location at which copy material is fed to the drum to a location beyond the transfer corona is mounted at the edge of the drum, so that a narrow strip of copy material extending along a side thereof moves over the stationary flexible band as the length of copy material moves under the transfer corona. At the point at which the copy material is to be removed from the surface of the drum, a struck up portion of the flexible strip moves a leading corner of the length of copy material away from the drum and into the nip between a turn roll and a rubber belt, a portion of the length of which extends around and into contact with the surface of the turn roll. The turn roll is driven in cooperation with the belt to carry the developed sheet away from the photoconductive drum toward conveyor rollers which deliver the sheet to the user of the machine. This pickoff arrangement is illustrated in and is more fully described in Ariyama U.S. Pat. No. 3,936,045, for "Sheet Stripping Device for Copying Apparatus".
After the photoconductive surface leaves the pickoff station described hereinabove, it next moves through a cleaning station at which a sponge roller in engagement with the surface of the drum is driven in such a direction that the engaging surface portions of the roller and the drum move in opposite directions. This sponge roller normally is wet with developer to facilitate the cleaning action and to prevent scratching of the drum surface by toner particles which remain on the roller when the developer dries.
While the machine described above functions satisfactorily in most instances, it incorporates a number of serious disadvantages. First, it will readily be apparent from the description of the pickoff system described hereinabove, that the copy sheet can have no image transferred thereto over the space along the edge thereof which rides over the flexible band extending through the transfer station. Thus, where the original carries information or printing in this area, it will not appear on the copy. Attempts to obviate this problem by minor modifications for directing the corner of the sheet into the nip between the turn roller and the belt without the use of a strip extending through the transfer station have not proved successful since any developed image in the strip which formerly was blank become smeared or dirtied. Another defect of the machine described hereinabove arises in connection with accidental double feeding of copy sheets from the supply to the drum. The first of the two sheets will be picked off by the pickoff device but often times the second sheet misses the pickoff. When this occurs the sheet may continue to travel around with the drum and become wrapped around the cleaning roller and ultimately soaked with developer, so as to assume a dark appearance so as not to be readily discernible. In such an instance upon continued use of the machine, the sheet wrapped around the cleaning roller scratches the surface of the photoconductor and ultimately may require replacement of the photoconductive drum. This member is one of the more expensive components of the machine.